I am not sure what the right way is because as I said, we can’t look at the flex position because that isn’t necessarily our 12th player. At the end of the day our lowest score drops off, and for me that wasn’t much. I imagine that better teams had a higher amount of points drop off, so it is more of a levelling out between stronger and weaker teams. However, the points benefit seems so low, I do wonder about its value on points scoring. It is more a help for team set up and player flexibility over points advantage.
I am not sure if I am missing your point however you are certainly missing mine. I am not saying the "flex" position is your 12th selected player if that is what you mean. I agree the flex position will likely never be the 12th fielded player. Furthermore, inherently the lowest score of the 12 "won't be much" but the question is what score came on field to replace that lowest score and that will rarely be the 11th highest score (which is the comparison you make).
To illustrate my point let's use your round 1 team.
Fielded DGR - Stoinis, Curran, Harper, Sutherland, JFM, Webster, McKenzie, Zampa
Fielded SGRs - Richardson, Connolly, Edwards, Overton
Lets assume that if the flex position didn't exist then you would have fielded 11 of these 12 players. Which of those players is not on field? I doubt it would have been one of your DGRs so it would have been 1 of your SGRs. Those players scored between 75 and 103. Zampa was the actual lowest score with 36 points. That means the ability to put a 12th player on field improved your score between 67 points (103-36) and 39 points (75-39) that round.
Your round 2 team probably illustrates the point even better.
Fielded DGR - Overton, Short, Bazley, Scott, Connolly, Turner, Richardson, Thornton
Fielded SGRs - Sutherland, Harper, Curran, Edwards
Richardson was your dropped score on 7 and he would have absolutely been in your starting 11 in a DGR. Your 4 SGRs scored between 30 and 65 so assuming you benched one of those it means your scored improve by between 58 points (65-7) and 23 points (30 - 7) due to the flex position.